Alkaline batteries that use low-cost, nonflammable aqueous electrolyte offer a significant advantage over organic electrolyte based batteries in terms of safety, flexibility in vehicle design and system cost reduction. For example, nickel/metal hydride (Ni-MH or NiMH) batteries are rechargeable alkaline batteries that have been widely used in electric vehicles (EVs) and hybrid electric vehicles (HEVs), such as the Toyota Prius®. NiMH use positive electrodes of nickel hydroxide (Ni(OH)2), like NiCd, but the negative electrodes use a hydrogen-absorbing alloy instead of cadmium. A NiMH battery can have two to three times the capacity of an equivalent size NiCd, and their energy density approaches that of a lithium-ion cell. However, the Ni-MH battery technology currently has two drawbacks. The first problem is its high cost per kilowatthour (kWh). The hydrogen-absorbing alloy used as the negative electrodes contains rare earth metals. There is growing concern that the world may soon face a shortage of the rare earth metals due to the scarcity of rare earth elements, which makes the whole battery expensive and limits the large-scale adoption of Ni-MH for EVs. The second problem is the high self-discharge issue and poor low-temperature performance, which is intrinsically related to the hydrogen-absorbing alloys used in the negative electrode. The metal hydride (MH) electrode needs to maintain certain H2 pressure, which could lead to the issue of high self discharge. The poor low-temperature performance of NiMH is also rooted from the slow diffusion of hydrogen atoms at low temperatures.
It is desirable to have improved alkaline batteries that address these abovementioned drawbacks.